The field of medical catheters has developed to allow the minimally invasive introduction of surgical tools, diagnostic fluids, medicaments or other materials into the vessels and cavities of the body. Various catheters are commercially available which offer a variety of features, such as steering capability, multiple lumens for the insertion of surgical tools or medicaments, etc. Examples of such catheter systems may be found in U.S. Pat. No. 4,983,165 to Loiterman for "Guidance System For Vascular Catheter Or The Like," U.S. Pat. No. 4,934,340 to Ebling et al. for "Device For Guiding Medical Catheters and Scopes," and U.S. Pat. No. 4,930,521 to Metzeger et al. for "Variable Stiffness Esophageal Catheter."
An especially important feature of a catheter system is the ability to measure the internal pressure within the space in which the catheter is operating. For example, the procedure of myeloscopy requires exploring the epidural space of the spinal column. Saline is infused under pressure to enlarge the epidural space by distending the layers of tissue that cover the dura. This pressure must be carefully monitored and controlled within defined parameters for the procedure to succeed. The pressure defined by the "safety zone" minimizes venous circulation while allowing arterial circulation to continue. This prevents ischemia to the spinal tissue and avoids rupturing frail venules which otherwise cloud the field of view of the procedure.
Similarly, in a cardiac catheterization, one of the first procedures that the physician performs is to connect a remote pressure sensor to the catheter to monitor the patient's blood pressure throughout the operation. This pressure sensor detects the patient's cardiac output and after-load. The pressure reading ensures the physician that the cardiac arteries remain at a pressure within the defined "safety zone," allowing him to perform a procedure, such as angloplastic dilation, while observing and maintaining an appropriate blood pressure level.
Many commercial catheters are provided with a proximal hand-held catheter housing which contains a steering mechanism for guiding the distal end of the catheter tube with one hand. Examples of these may be seen in the PCT Patent Application No. WO 91/11213 of Lundquist et al. entitled "Catheter Steering Mechanism," European Patent Application No. 370,158 of Martin entitled "Catheter For Prolonged Access," and U.S. Pat. No. 4,737,142 to Heckele entitled "Instrument For Examination and Treatment of Bodily Passages."
A pressure sensing feature may be adapted for a catheter. The internal pressure of the vessel or cavity is sensed through the lumen of an elongated catheter tubing, extending from the distal end of the catheter to a remote pressure sensitive membrane. The pressure reading is then displayed on a large, remote monitor. This type of "closed" catheter system is useful for procedures involving a vessel or cavity with a preexisting osmotic pressure, such as for monitoring blood pressure in an angioplasty.
Catheters currently available may be constructed of an elongated polymer coated tube with at least one lumen extending longitudinally therein. In order to create a catheter possessing variable stiffness, such that the distal tip is more flexible to assist in controlling the direction of insertion, catheters may be constructed of two separate tubings of different thicknesses, which are consecutively fused together, end-to-end, at a junction.
Additionally, some catheters offer a steering mechanism which involves affixing wires within opposing lumens of the catheter and anchoring the proximal ends of the wires within the catheter housing through a pin wheel tension configuration. There are several problems presented by these present systems.
In the commonly known catheters, which are adapted to sense internal pressure, the pressure monitoring system often becomes clogged by tissues and debris, such as blood clots, or disrupted by air bubbles, because of the extensive amount of pressure tubing and numerous valves required to traverse the distance from the catheter to the remote pressure sensor and monitor. Such obstructions result in inaccurate pressure readings, which threaten the safety of the patient. Under critical cardiac operating conditions, for example, a single air bubble may cause the monitor to display very similar systolic and diastolic blood pressures, forcing the physician to terminate the procedure.
Finding the source of the disruption in pressure reading is unnecessarily difficult. The clog or air bubble could be anywhere in the extensive tubing, the remote sensor element, or in the multiple interconnecting manifolds. Since locating and removing clogs and/or air bubbles in the pressure tubing is time consuming, this greatly increases the risk of the surgical procedure for the patient.
Moreover, the remote position of the pressure monitor forces the physician to look away from the surgical field, and especially the distal end of the catheter, to check the patient's internal pressure. This further heightens the potential risks of performing a catheterization.
Additionally, it is laborious and expensive to construct the catheter tube itself by fusing together extensive polymer tubes of differing thicknesses. The spliced tube junction must align the lumens, be carefully smoothed on the outside, yet remain strong, so as to not interfere with steering the catheter into a vessel or cavity.
Furthermore, the guide wire steering mechanism of current catheter models does not provide an optimum degree of sensitivity for the control and manipulation of the catheter. The currently available steering mechanisms require the operating physician to maintain his hand in an awkward, palm-up position.